Defrost control



1962 A. A. MATTHIES DEFROST CONTROL 2 Shets-Sheet 1 Filed Jan. 5, 1961 INVENTOR. ALAN ARTHuRMATTmEs BYgyfll Z Fm. Z

ATTORNEY Patented Nov. 13., 1952 3,063,249 DEFROST CONTROL Alan Arthur Matthies, Milwaukee, Wis., assignor to Coutrols Company of America, Schiller Park, 111., a corporation of Delaware Filed Jan. 5, 1961, Ser. No. 86,883 20 Claims. (Cl. 62-440) This invention relates to an improved frost sensor and defrosting system for a refrigerator, cooler or freezer.

In my copending applications, Serial No. 1,316, filed January 8, 1960, and Serial No. 53,172 filed August 31, 1960, defrost systems were disclosed which sensed the coils of a refrigerator by cycling a sensing member into and out of engagement with the coil of a refrigerating system by the energization of a heat motor. If a prede termincd amount of frost was sensed, a defrost cycle would be initiated, after which a refrigeration cycle would be commenced. It has been found that if the 'refrigerator fan is actuated after a defrost cycle simultaneously with the start of a refrigeration cycle, the refrigerator temperature rises due to the circulation of the hot air which surrounds the coils of the refrigerator after the defrost cycle.

An object of the present invention is to minimize the refrigerator ambient temperature rise after a defrost cycle.

This object is accomplished by delaying the actuation of the circulating fan through the use of a second heat motor which is responsive to the refrigerator ambient. In my prior designs the circulating fan switch was closed simultaneously with the opening of the defrost cycle switch while in the present design the second heat motor prevents closure of the circulating fan switch until the refrigerator ambient has been lowered to a predetermined level.

A further object is to provide a defrost switch which can be manufactured at lower cost and can be easily calibrated in the field to sense a predetermined frost thickness.

In the prior devices, the calibration of the switches was accomplished by running the frost sensor through an actual heating cycle, and these settings could not be readily reset once the control has been installed. In the present invention the control is provided with an adjusting screw which allows user-selection of the thickness of frost which will actuate the control by a procedure which is simple and rapid and requires no cycling of the control. low lower cost manufacture.

Other objects and advantages will be pointed out in, or be apparent from, the specification and claims, as will obvious modifications of the single embodiment shown in the drawings, in which:

FIG. 1 is a top view of the defrost switch with the cover removed;

FIG. 2 is taken on line 22 of FIG. 3;

FIG. 3 is taken on line 3--3 of FIG. 2; and

FIG. 4 shows the circuit for the present system.

As seen in the drawings, the housing of the frost sensor is mounted on bracket 12 which is clamped on coil M of the refrigerating system. To maintain an accurate distance for the movement of sensing member 16, end 18 of the bracket is used as a frost accumulating surface with screen 20 wrapped on the surface to dissipate any moisture which may accumulate thereon during a defrost action. The bracket is clamped tightly to one of the coils of the refrigerating system by bolts 25, so that the same temperature conditions will exist on the bracket as are encountered on the coil. Leaf springs 22, 24 and 26 are secured to the housing by bolts 28, 30 and Further, the design has been cleaned up to alh 3'2 and are interconnected by bridge 34. The leaf springs are normally biased toward the coil from the connection with the housing to the bridge. Center spring 24 projects outward from the bridge so that it will engage sensing member 16 and carries permanent magnet 36 and common contact 38. The sensing member is biased by spring 54 to follow the motion of the center spring. It can be seen that the bias of the leaf springs will normally hold the sensing member against the coil in a sensing position.

The leaf springs are moved away from the coil by bimetal 40 which is secured to the housing by screws 42 and engages set screw 44 in the bridge. A boot 45 made of Teflon (tetrafluorethylene) is placed on the end of the set screw to eliminate any friction between the set screw and bimetal. The bimetal is heated to move away from the coil by energizing heater 48 secured to the housing by screw 50 within semicircular portion 52 of the bimetal. The motion of the bimetal away from the coil will move the center spring into engagement with an adjustable permanent stop 55 provided in cover 56, allowing the sensing member to move to a non-sensing position.

Leaf spring 26 carries permeable member 58 and defrost switch contact 60 and is bent upward at the bridge to bias the defrost switch contact away from the center spring. Leaf spring 22 carries permeable member 62 and fan switch contact 64 and is bent downward from the center spring to bias the fan switch contact away from the center spring. The magnet is provided with suflicient magnetic force to overcome the bias of one of the leaf springs and hold the switch contact carried by that spring against the common contact, but does not have sufficient magnetic force to overcome the bias of both springs simultaneously. If one of the contacts is held against the common contact by the magnet and the other contact is brought into engagement with the magnet and the com mon contact, the first contact will be released, since the magnetic force of the magnet will be split between the two permeable members and will therefore be insufficient to hold the first contact.

In operation, the fan switch is normally closed when the bimetal is de-energized and the center spring moves the sensing member into engagement with the screen. If the sensing member engages a predetermined amount of frost on the screen, the end of the center spring will be stopped by the sensing member and the center spring will bend, bringing the defrost contact into engagement with the common contact and magnet. Bending of the center spring will increase the bias of leaf spring 22, and the division of magnetic flux between the two permeable members will cause the leaf spring to open the fan switch. When the bimetal is energized, a defrost cycle will be initiated and the bimetal will push the bridge and leaf springs away from the coil. The end of the center spring will engage permanent stop 55, causing the center spring to bend upward in the middle. Normally, the fan switch will close against the common contact and the defrost switch will snap open into recess 66 in the cover.

In order to delay the closing of the fan switch after a defrost cycle, bimetal 68 is secured to the cover and engages plunger 70 which projects through the cover and engages the end of leaf spring 22. This bimetal is responsive to the ambient temperature of the refrigerator and will move toward the coil as the refrigerator temperature rises. When bimetal 40 pushes the center leaf spring against permanent stop 55, plunger 70 will stop the upward motion of leaf spring 22. The center leaf spring will bend in the center, causing an increase in the bias of leaf spring 26. When the bias of leaf spring 26 has increased sufficiently to overcome the holding force of the magnet, the defrost switch will be opened stopping defrost action and starting a refrigerating cycle. As the refrigerator temperature starts to fall, bimetal 68 will warp away from the coil, allowing the fan switch contact to move into contact with the common contact due to the bend in the center spring to start the circulating fan.

As seen in FIG. 4-, heater 48 for the defrost switch is connected in parallel with compressor 72 across the line L L When compressor relay switch 74 is closed, the compressor and heater will be energized. Bimetal iii will warp away fro-m the coil, pushing the bridge and center leaf spring away from the coil, with sensing member 16 following the motion of the center leaf spring. If the common contact is in engagement with fan switch contact 6%, fan '76 will start to operate when the compressor is energized. If, however, the common contact is in engagement with the defrost switch contact, the solenoid action defrost device 78 will be energized so that the compressor is initially run through a defrost cycle. At the end of a defrost cycle, the compressor will start a refrigerating cycle. Since the refrigerator coils are filled with hot gas at the end of a defrost cycle, hot air will surround the coils until the refrigerant in the coils has been cooled by the compressor. Bimetal 68 will then warp away from the coil, allowing the fan switch contact to engage the common contact energizing the circulating fan.

The defrost switch is calibrated by removing cover 56 and placing block 8t (shown dotted) on the screen. The block represents the thickness of frost at which a defrost cycle is to be started. With the defrost switch open, set screw 44 is backed out of the bridge until the defrost switch contact closes with the common contact. This arrangement provides an easy and reliable means of setting the defrost switch to start a defrost cycle for any thickness of frost.

This particular arrangement provides a number of advantages, one of which is that the sensing member will be moved out of contact with the coil during both refrigerating and defrosting cycles, thereby preventing any frost or moisture from forming on the sensing plunger. It also provides control of the refrigerator fan, so it is turned off during the defrost action to minimize the temperature rise in the refrigerator. This delay will allow the compressor to refrigerate the coils and remove most of the excess heat from the immediate vicinity surrounding the coils before recirculation of air begins.

Although but a single embodiment of the present invention has been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

I claim:

1. A defrost control for a refrigerating system including a defrost device and a circulating fan comprising, sensing means movable between a sensing position and an inoperative position, motor means controlling the motion of the sensing means, means actuated by the motion of the sensing means to either actuate the defrost device or the circulating fan, and means for delaying the actuation of the circulating fan after the defrost device has completed a defrost cycle.

2. A defrost device according to claim 1 wherein said delaying means for controlling the actuation of the circulating fan comprises a bimetal responsive to the ambient temperature of the refrigerator.

3. A defrost device according to claim 2 wherein said motor means includes a second bimetal energized simultaneously with the refrigerating system.

4. A defrost control for a refrigerating system includin: a compressor, defrost device and circulating fan comprising, sensing means movable between a sensing position and an inoperative position, bimetal means controlling the motion of the sensing means, a heater for the bimetal means actuated simultaneously with the compressor to warp the bimetal means to move the sensing means from one position to the other, said sensing means being biased to follow the l .otion of the bimetal, switch means actuated by the motion of the sensing means to control the defrost device and the circulating fan, and second bimetal means responsive to the ambient temperature of the refrigerator to delay actuation of the circulating fan after the defrost device has completed a defrost cycle.

5. A defrost control for a refrigerating system having, a compressor, a defrost device, a circulating fan and a frost accumulating surface comprising, a sensor positioned to engage the surface, means for moving the sensor toward and away from the frost accumulating surface, first switch means carried by the moving means to actuate the fan, magnetic means normally holding the first switch closed, second switch means carried by the moving means to control the defrost device, said second switch means closing when the sensing means engages a predetermined thickness of frost on the surface, said magnetic means releasing the first switch means and holding the second switch closed when the second switch is closed by the sensing means, said first switch means normally closing and said second switch means normally opening at the end of a defrost cycle by the motion of the moving means, and means for delaying the closing of the first switch.

6. A defrost control according to claim 5 wherein said moving means includes spring means normally biasing the sensing means towards the frost accumulating surface, and a heat motor means for moving the spring means away from the surface when the compressor is energize 7. A defrost control according to claim 6 wherein the delaying means includes a bimetal responsive to the refrigerator ambient temperature to delay the closing of the first switch means until the ambient temperature has reached a predetermined minimum.

8. A defrost control according to claim 7 wherein said first and second switch means are carried by the spring means.

9. The combination of a refrigerating system including a circulating fan and a defrost control comprising, a compressor, an electric circuit for the compressor, a fan in a parallel circuit to the compressor, an electrically energized defrost device in a parallel circuit to the compressor, switch means for energizing either the fan or the defrost device, sensing means mounted for motion towards and away from the system evaporator for sensing frost on the evaporator, heat motor means controlling the motion of the sensing means, said sensing means controlling the operation of the switch means, and second heat motor means for delaying the operation of the fan after a defrost cycle until a predetermined ambient temperature is reached.

16. The combination according to claim 9 wherein the heat motor means includes a spring biased in a sensing direction and a bimetal positioned to move the spring away from the evaporator when the bimetal is heated.

11. A defrost control for a refrigerating system including a compressor, a defrost device and a circulating fan comprising, a frost accumulating surface, a housing mounted adjacent the surface, a sensor mounted in the housing and movable into engagement with the surface, spring means secured to the housing and operatively engaging the sensor, a bimetal engageable with the spring means, said spring means being biased to follow the motion of the bimetal, a heater mounted within the housing to heat the bimetal so that the bimetal moves the spring means and sensor, means for energizing the heater simultaneously with the compressor to move the spring and sensor away from the surface, means for limiting the motion of the spring means away from the surface, said sensor limiting the motion of the spring means toward the surface when a predetermined thickness of frost is sensed on the surface, and switch means carried by the spring means to actuate the defrost device if a predetermined thickness of frost is encountered on the surface and to de-activate the defr'ost device and activate the circulating fan after the limiting means is encountered.

12. A defrost control according to claim 11 including means for delaying the activation of the fan until the refrigerator ambient has reached a predetermined level.

13. A defrost control according to claim 12 wherein the fan switch and defrost switch are carried by and biased away from the spring means and are opened by increasing the bias of the switches away from the spring and closed by decreasing the bias of the switches away from the spring, said increasing and decreasing resulting from the bending of the spring means upon engaging the limiting means or the sensor.

14. A defrost control according to claim 13 including magnetic means carried by the spring means to hold the switches closed in the movement from one position to the other.

15. The combination with a refrigerating system including a compressor, a refrigerator fan and a defrosting device connected in-a common circuit, of means for controlling the operation of the fan and defrosting device in accordance with frost conditions on a portion of the refrigerating system comprising, sensing means positioned to engage a portion of the refrigerating system, spring means operatively positioned to bias the sensing means into engagement with the refrigerating system, heat motor means operatively engaging the spring means, anti-friction means secured to the spring means to prevent friction at the point of engagement with the heat motor means, heater means connected to the common circuit for heating the bimetal when the compressor is energized to move the bimetal through a prescribed path, said sensing member being moved away from the refrigerating system when the bimetal is energized and moving into engagement with the refrigerating system when the compressor is de-energized, switch means carried by the spring means for actuating the defrosting device when a predetermined accumulation of frost is sensed on the refrigerating system, and switch means for controlling the operation of the fan after a defrosting cycle has been completed.

16. A defrost control for a refrigerating system having a compressor, a defrost device, a circulating fan and a frost accumulating surface comprising, a sensor positioned to engage the surface, means for moving the sensor toward and away from the frost accumulating surface, fan switch means carried by the moving means, magnetic means for maintaining the fan switch means in an operative position, defrost switch means carried by the moving means, the defrost switch means being operative to energize the defrost device in response to the sensor engaging a predetermined thickness of frost on the surface, said magnetic means releasing the fan switch means to an inoperative position and maintaining the defrost switch means in an operative position when the sensor engages a predetermined thickness of frost, the fan switch means being normally moved to an operative position by the motion of the moving means, the defrost switch means moving to Ian inoperative position by the motion of the moving means, and means for delaying the movement of the fan switch means to the operative position until the ambient temperature of the refrigerator has reached a predetermined minimum.

17. A defrost control according to claim 16 wherein the moving means includes a bimetal heated in response to energization of the compressor and the delaying means includes a heat motor responsive to the ambient temperature of the refrigerator.

18. A control device comprising, a sensing means, means biasing the sensing means in a sensing direction, heat motor means for relieving the bias on the sensing means so that it can move in a non-sensing direction, means limiting the motion of the bias means in the non- .sensing direction, first switch means closed by the bias means in response to a predetermined restriction in the movement of the sensing means in the sensing direction, and opened by the motion of the bias means in the nonsensing direction, after engaging the limiting means, and second switch means normally closing simultaneously with the opening of the first switch means.

19. A control device according to claim 18 including heat motor means for delaying the closing of the second switch means after the first switch means has opened.

20. A control device comprising, a sensing means, means biasing the sensing means in a sensing direction, heat motor means for relieving the bias on the sensing means so that it can move in the non-sensing direction, first switch means closed by the bias means in response to a restriction in the movement of the sensing means in the sensing direction, adjusting means carried by the biasing means to vary the closing of the first switch in accordance with a predetermined restriction, said first switch means being opened by the motion of the bias means in the non-sensing direction after engaging the limiting means, and second switch means normally closing simultaneously with the opening of the first switch means.

References Cited in the file of this patent UNITED STATES PATENTS 2,064,010 Hull Dec. 15, 1936 2,662,380 Sutton Dec. 15, 1953 2,713,249 Schordine July 19, 1955 

